Studies in our laboratories have demonstrated that the intimal thickening seen in coronary artery bypass vein grafts in dogs is reduced by administration of the platelet inhibiting drugs: dipyridamole and aspirin. We have also demonstrated that the location of platelet deposition in these grafts can be accurately estimated from scientiphotos obtained from a gamma camera following the intravenous infusion of autologous Indium-111 labeled platelets. Based on the data obtained from the above studies and using the same model we propose to further investigate the sequential processes leading to graft occlusion and the mechanisms involved in the apparent beneficial effect of platelet inhibiting drugs in the canine model by: 1) quantifying platelet deposition with Indium-111 labeled platelets, 2) evaluation of alteration in endothelial permeability with 131I-idodo-cholesterol, (3) determining tissue and blood level of dipyridamole with 14c-dipyridamole and, 4) quantifying endothelia and smooth muscle cell proliferation with 3H-thymidine. Quantitative histological measurements and ultrastructural analyses of endothelial cell loss, platelet adhesion and intimal proliferation in the bypass graft will also be preformed.